1. Field of the Invention
The present invention relates to a recording material, and more particularly, to a recording material capable of being recorded upon with a thermal head or the like.
2. Description of the Related Art
Heat-sensitive recording materials, on which images can be recorded by applying heat from a thermal head, have been significantly developed in recent years. This is due to the fact that such materials possess many advantages, particularly in that the recording apparatuses therefor are simple, reliable, and relatively maintenance-free. Conventional recording materials contain a support having a recording layer thereon containing coloring components, such as a combination of an electron donating dye precursor and an electron accepting compound, and a combination of a diazonium salt compound and a coupler. Images are recorded by utilizing the coloring component reactions, which proceed with the application of heat.
Because image formation is executed by applying heat in the heat-sensitive recording method, the surface temperature of the recording material is high during image recording. Furthermore, the recording material is pressed during image recording when a contact-type recording means, such as a thermal head, is used. At this time, water vapor and air in the recording layer expand due to the applied heat, and when the vapor and air migrate to the surface of a coating layer of the support, they expand on the coating layer to form gaps, or blisters. The formation of blisters causes deterioration in glossiness and in the image quality of the recorded image.
In order to suppress surface blisters, the formation of a layer having low permeability to gaseous water vapor, such as an undercoating layer, between the support and the recording layer has been known. The undercoating layer preferably contains a water-soluble resin, such as polyvinyl alcohol, as a binder. Furthermore, when the undercoating layer containing polyvinyl alcohol is formed on the support, the surface of the coated layer becomes flat by leveling after coating. Therefore, it is preferable to utilize a method that uses a coating solution for the undercoating layer, prepared by dissolving polyvinyl alcohol in water and then adding methanol or the like thereto.
However, even when such an undercoating layer containing polyvinyl alcohol is provided, there are cases where cracks are formed therein by physical force, and where gaseous water vapor reaches the support through the cracks to form blisters.
When the above-described recording material, which has a recording layer on a support, is immersed in water, there are cases when the recording layer is released from the support. Hence, there is a demand for improvement in water resistance and for better adhesiveness of the recording layer to the support in wet conditions.
In order to improve the water resistance and the adhesiveness of the recording layer, the formation of an undercoating layer containing a water-soluble resin, such as polyvinyl alcohol, and a hardening agent between the support and the recording layer has been known. However, there are cases where the addition of a hardening agent increases the viscosity of the coating composition for the undercoating layer and this causes problems when the undercoating layer is formed.